This invention relates generally to devices and methods that are used to test viscosified fluids, especially ones containing particulate material (subsequently referred to simply as xe2x80x9cparticulatexe2x80x9d). The particular field of use is the oil and gas industry.
Various types of fluids are used in the oil and gas industry. Non-limiting examples include drilling muds, cement slurries, and stimulation treating fluids. Such fluids are typically pumped into oil or gas wells in known manners. It is desirable to know various characteristics of the fluids to determine how such fluids will act upon being pumped and placed in, or circulated through, the wells.
Viscosity, elasticity, and consistency are rheological characteristics that sometimes need to be measured for a given fluid. Known devices used to test fluids for these characteristics include viscometers, rheometers, and consistometers.
Some fluids used in oil or gas wells carry particulate, and it is typically desired that such fluids support the particulate in suspension for at least some period of time. That is, the particulate is preferably dispersed throughout the volume of a particular fluid during at least part of the time the fluid is used in a well. For example, a fracturing fluid might include a base fluid in a gel form and a quantity of particulate referred to as a propping agent or proppant. An example of a propping agent or proppant is sand. The base fluid preferably supports the proppant such that the proppant is suspended in the fluid during the time the mixture is pumped into a well. The pumping is under pressure sufficient for the fluid to hydraulically fracture a selected zone of the earth traversed by the well. After fracturing, the fluid may be flushed out with the flow of hydrocarbons from the fractured zone, but the propping agent preferably remains in place to prop the fractures open.
A typical fluid used to transport particulate has a viscosity that changes during the time the fluid is used in a well. Viscosity is defined as the ratio of shear stress to shear rate (velocity gradient). If this ratio changes with shear rate, this may be referred to as xe2x80x9capparent viscosity function.xe2x80x9d Viscosity is one parameter of the fluid that defines the fluid""s ability to support the particulate in suspension. However, to measure a single viscosity point or the apparent viscosity function does not directly indicate the time during which the fluid will support particulate in suspension and the time during which the fluid will not. That is, a measurement that merely shows a changing viscosity does not indicate when the particulate is in suspension within the fluid and when it is not (i.e., when the particulate has settled out of the fluid). Thus, there is the need for a device and method which can test fluids to determine times during which particulate is suspended in the fluid and times during which particulate settles out of suspension. There is the more particular need for a device and method to measure the viscous and elastic properties of a fluid, both with and without particulate, under dynamic conditions at elevated temperatures and pressures at a variety of shear rates and in such a way as to directly indicate particle transport, suspension and settling. At least one embodiment of such a device and method preferably should also be suitable for use at a well site to measure crosslink time of a fluid being pumped into the well.
The present invention meets the foregoing needs by providing a novel and improved device and method for testing viscous and/or elastic fluids, including ones containing particulate. Such device and method directly indicate time periods during which a tested fluid is supporting particulate in suspension and when the tested fluid is not (i.e., when the particulate is settling out of suspension).
A particular implementation of the device of the present invention may be referred to as a high-pressure, high-temperature mixer viscometer that can measure viscous and elastic properties and crosslink and particulate transport time. This implementation includes a paddle type of mixing device which has one or more flags, paddles, or vanes which rotate in or around the fluid to be tested and two or more flags, paddles or vanes in a torque sensing structure. The device is capable of measuring varying volume average shear rates and volume average shear stresses, signifying varying viscosities, and is especially useful at low shear rates. This device can condition the fluid under test at low, ambient, and elevated temperatures and pressures. This device provides an output that can be used to measure or indicate viscous and elastic properties of the test fluid (which can be with or without particulate material), the change in fluid properties with time (e.g., crosslink time), particle transport (particle suspension and particle settling), and particle-to-particle interactions and degree of adhesive coating on particles (e.g., higher torque readings for more particle-to-particle interaction, such as from higher particle concentrations, or for increased adhesive coating).
The present invention provides a mixer viscometer which comprises: a receptacle having a cavity to receive a viscosified fluid containing particulate; means for closing the cavity after viscosified fluid containing particulate is placed therein such that the closed cavity defines a continuous test chamber which can be pressurized above atmospheric pressure; means for stirring the fluid in the test chamber such that particulate in the fluid is suspended in the fluid during one period of time of the stirring but is not suspended in the fluid during another period of time of the stirring; and means for generating a signal in response to the stirring during both periods of time. The means for stirring preferably includes at least one projection extending into the cavity from an inner surface of the receptacle defining the cavity.
Another definition of the present invention is as a particle transport capability detector apparatus which comprises: a viscometer including a viscometer cup and further including an axial shaft disposed within the cup when a fluid to be tested is in the cup; at least two projections extending laterally outward from the axial shaft of the viscometer; and at least one projection extending laterally inward from an inner surface of the viscometer cup, wherein the projections effect stirring of fluid in the cup in response to rotation of at least one of the cup or axial shaft of the viscometer.
A viscometer test chamber of the present invention comprises: a slurry cup; a pressure-sealed end closure for the slurry cup; a support hanging below the end closure into the slurry cup when the end closure is connected to the slurry cup to close the slurry cup; not more than four vertical planar projections extending laterally outward from the support; and not more than four vertical planar projections extending laterally inward from an inner surface of the slurry cup, wherein the projections effect stirring of fluid in the slurry cup in response to rotation of at least one of the slurry cup or support.
The present invention also provides a method of testing for particulate transport time of a fluid containing particulate. The method comprises stirring, for a time during which the viscosity or elasticity of the fluid changes, a fluid containing particulate such that during a first period of the stirring time substantially all the particulate remains suspended in the fluid and during a second period of the stirring time substantially all the particulate settles out of suspension in the fluid. The method further comprises generating a signal during the first and second periods such that the signal has a characteristic that changes from the first period to the second period to indicate the change in particulate carrying ability of the fluid.
The method of the present invention can also be defined as comprising: using in a high-pressure, high-temperature viscometer a container having at least one inward projection and using in the viscometer an axial support having at least two outward projections, wherein the container holds a viscous and/or elastic fluid containing particulate and the support extends into the fluid; creating relative movement between the container and the support, and the projections thereof; and generating a measurement signal in response to a characteristic of the viscometer occurring by creating the relative movement such that the measurement signal indicates an elastic particulate transport time period and a viscous settling time period. In a particular implementation, generating a measurement signal includes generating an electric signal in response to torque related to creating relative movement between the container and the support and the projections thereof. The measurement signal also may indicate, prior to the elastic particulate transport time period and the viscous settling time period, a crosslinking time during which the fluid becomes viscoelastic.
Still another definition of the method of testing a viscosified fluid containing particulate comprises: mixing sand and a basegel to form a sand-gel slurry mixture; putting at least a portion of the mixture in a slurry cup having at least two inward projections extending inward from an inside surface of the cup; connecting the slurry cup in a viscometer having an axial support from which at least two outward projections extend outward; increasing pressure in the connected slurry cup such that pressure on the mixture in the cup is greater than atmospheric pressure; creating relative movement between the slurry cup and the axial support, and the projections thereof, such that the projections impart a stirring force in the fluid under pressure; and generating a measurement signal in response to a characteristic of the viscometer occurring by creating the relative movement. The method may further comprise heating the mixture in the slurry cup to a temperature greater than ambient temperature (and preferably greater than 212xc2x0 F.).
Still a further definition of the present invention is as a method of testing a fluid containing particulate, comprising: using in a viscometer a cup having at least one inward projection and using in the viscometer an axial support having at least two outward projections, wherein the cup receives fluid containing particulate and the support extends into the fluid; creating relative movement between the cup and the support, and the projections thereof; and generating a measurement signal in response to a characteristic of the viscometer occurring by creating the relative movement such that the measurement signal indicates a crosslinking time for the fluid. The method of the present invention may further comprise placing in the container at a well site a sample of the fluid taken from a stream of the fluid as the stream is flowing into the well, and performing the using, creating and generating steps at the well site as the stream is flowing into the well.
Therefore, from the foregoing, it is a general object of the present invention to provide a novel and improved device and method for testing viscous and/or elastic fluids, including ones containing particulate. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art when the following description of the preferred embodiments is read in conjunction with the accompanying drawings.